Display device

ABSTRACT

In an optical system, a first optical section having positive power, a second optical section provided with a first diffractive element and having positive power, a third optical section having positive power, and a fourth optical section provided with a second diffractive element and having positive power are disposed along a light path of image light emitted from an image light generation device. A first intermediate image of the image light is formed between the first optical section and the third optical section, a pupil is formed in the vicinity of the third optical section, a second intermediate image of the image light is formed between the third optical section and the fourth optical section, and the fourth optical section collimates the image light to form an exit pupil. The first diffractive element and the second diffractive element are in a conjugate relation or a roughly conjugate relation.

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. application Ser. No.16/257,109, filed Jan. 25, 2019, the contents of which are incorporatedherein by reference.

BACKGROUND 1. Technical Field

The present invention relates to a display device for displaying animage using a diffractive element.

2. Related Art

As a display device using a diffractive element such as a holographicelement, there is proposed a device for deflecting image light havingbeen emitted from an image light generation device toward the eyes of anobserver using the diffractive element. In the diffractive element,interference stripes are optimized so that an optimum diffractive angleand diffractive efficiency can be obtained at a specific wavelength.However, since the image light has predetermined spectrum width centeredon the specific wavelength, the light at a peripheral wavelength shiftedfrom the specific wavelength becomes a factor for degrading theresolution of the image. Therefore, there is proposed a display devicein which the image light having been emitted from the image lightgeneration device is emitted toward a second diffractive elementdisposed on the front side using a first diffractive element of areflective type, and then the image light having been emitted from thefirst diffractive element is deflected toward the eyes of the observerusing the second diffractive element. According to such a configuration,it is possible to perform wavelength compensation using the firstdiffractive element, and it is possible to prevent the degradation ofthe resolution of the image due to the light at the peripheralwavelength shifted from the specific wavelength (see JP-A-2017-167181(Document 1)). Further, there is proposed a display device provided withtwo diffractive elements designed so as to compensate an applicationerror with each other (see JP-A-2004-318140 (Document 2)). Further,there is proposed a technology for preventing occurrence of anaberration and a color shift using two diffractive elements in aneyepiece optical system (see JP-A-08-184779 (Document 3)).

However, in the technologies disclosed in Documents 1, 2 and 3 describedabove, since there is a possibility that the wavelength compensationcannot sufficiently be achieved by the two diffractive elements, afurther improvement has been desired.

SUMMARY

An advantage of some aspects of the invention is to provide a displaydevice capable of appropriately performing the wavelength compensationusing the two diffractive elements.

A display device according to a first aspect of the invention includes afirst optical section having positive power, a second optical sectionprovided with a first diffractive element and having positive power, athird optical section having positive power, and a fourth opticalsection provided with a second diffractive element and having positivepower, the first optical section, the second optical section, the thirdoptical section and the fourth optical section are disposed along alight path of image light emitted from an image light generation device,a first intermediate image of the image light is formed between thefirst optical section and the third optical section, a pupil is formedbetween the second optical section and the fourth optical section, asecond intermediate image of the image light is formed between the thirdoptical section and the fourth optical section, and an exit pupil isformed in the light path on an opposite side of the fourth opticalsection to the third optical section.

According to the display device according to the first aspect, the firstintermediate image of the image light is formed between the firstoptical section and the third optical section, the second intermediateimage is formed between the third optical section and the fourth opticalsection, and the pupil is formed in the vicinity of the third opticalsection. Therefore, it is possible to image the light beam emitted fromone point of the image light generation device on the retina as onepoint, and at the same time, make the entrance pupil of the opticalsystem and the pupil of the eyeball have a conjugate relation, andfurther, make the two diffractive elements (the first diffractiveelement and the second diffractive element) have a conjugate relation ora roughly conjugate relation. Therefore, since the positions of thefirst diffractive element and the second diffractive element which thesame light beam enters correspond to each other, it is possible toappropriately perform the wavelength compensation using the twodiffractive elements.

The display device according to the first aspect may be configured suchthat the first intermediate image is formed between the first opticalsection and the second optical section. According to such an aspect, itis possible to perform more sufficient wavelength compensation than inthe case of forming the first intermediate image between the secondoptical section and the third optical section.

The display device according to the first aspect may be configured suchthat the third optical section arbitrarily controls the image lightemitted from the second optical section into diverging light, converginglight or parallel light, and then make the image light enter the fourthoptical section.

The display device according to the first aspect may be configured suchthat the third optical section makes light deflected by the firstdiffractive element to be shifted from light with a specific wavelengthenter a predetermined range of the second diffractive element withrespect to light corresponding to one point of an image generated by theimage light generation device. In the aspect of the invention, the“light corresponding to one point of the image generated by the imagelight generation device” corresponds to the light emitted from one pointof the display surface of the image light generation device shaped likea panel in the case in which the image light generation device is shapedlike a panel. In contrast, in the case in which the image lightgeneration device performs two-dimensional scan with the laser beamusing the micromirror device to thereby generate the image, the “lightcorresponding to one point of the image generated by the image lightgeneration device” corresponds to the light emitted from the micromirrordevice in one direction.

The display device according to the first aspect may be configured suchthat the second optical section makes the image light emitted from thefirst optical section enter the third optical section as converginglight.

The display device according to the first aspect may be configured suchthat a plane of incidence of the second diffractive element is aconcavely curved surface recessed in a central part from a peripheralpart, and the second diffractive element collimates the image lightemitted from the third optical section.

The display device according to the first aspect may be configured suchthat an absolute value of magnifying power of projection on the seconddiffractive element due to the third optical section of the firstdiffractive element is in a range from 0.5 times to 10 times. In thiscase, the absolute value of the magnifying power is preferably in arange from the same size to 5 times.

The display device according to the first aspect may be configured suchthat an optical distance between the first diffractive element and thethird optical section is shorter than an optical distance between thethird optical section and the second diffractive element.

The display device according to the first aspect may be configured suchthat the first diffractive element and the second diffractive elementare in a conjugate relation. Further, it is possible to adopt aconfiguration in which light emitted from a first position in the firstdiffractive element enters a range of ±0.8 mm with respect to a secondposition corresponding to the first position in the second diffractiveelement.

A display device according to a second aspect of the invention includesa first optical section having positive power and including a pluralityof lenses, a second optical section provided with a first diffractiveelement and having positive power, a third optical section havingpositive power, and a fourth optical section provided with a seconddiffractive element and having positive power, the first opticalsection, the second optical section, the third optical section and thefourth optical section are disposed along a light path of image lightemitted from an image light generation device, a first intermediateimage of the image light is formed in the light path between a firstlens located closest to the image light generation device out of theplurality of lenses in the first optical section and the third opticalsection, a pupil is formed between the second optical section and thefourth optical section, a second intermediate image of the image lightis formed between the third optical section and the fourth opticalsection, and an exit pupil is formed on an opposite side of the fourthoptical section to the third optical section.

According to the display device according to the second aspect, thefirst intermediate image of the image light is formed between the firstlens and the third optical section, the second intermediate image isformed between the third optical section and the fourth optical section,and the pupil is formed in the vicinity of the third optical section.Therefore, it is possible to image the light beam emitted from one pointof the image light generation device on the retina as one point, and atthe same time, make the entrance pupil of the optical system and thepupil of the eyeball have a conjugate relation, and further, make thetwo diffractive elements (the first diffractive element and the seconddiffractive element) have a conjugate relation or a roughly conjugaterelation. Therefore, since the positions of the first diffractiveelement and the second diffractive element which the same light beamenters correspond to each other, it is possible to appropriately performthe wavelength compensation using the two diffractive elements.

The display device according to the second aspect may be configured suchthat the first intermediate image is formed in the first opticalsection.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described with reference to the accompanyingdrawings, wherein like numbers reference like elements.

FIG. 1 is an appearance diagram showing an aspect of an appearance of adisplay device according to a first embodiment of the invention.

FIG. 2 is an appearance diagram showing an aspect of another appearanceof the display device.

FIG. 3 is an explanatory diagram showing an aspect of an optical systemof the display device.

FIG. 4A is an explanatory diagram of interference stripes of adiffractive element.

FIG. 4B is an explanatory diagram of another aspect of the interferencestripes of the diffractive element.

FIG. 5 is an explanatory diagram showing diffractive characteristics ofa first diffractive element and a second diffractive element.

FIG. 6A is an explanatory diagram of the case in which the firstdiffractive element and the second diffractive element are in aconjugate relation.

FIG. 6B is an explanatory diagram of the case in which the firstdiffractive element and the second diffractive element are not in theconjugate relation.

FIG. 6C is an explanatory diagram of the case in which the firstdiffractive element and the second diffractive element are not in theconjugate relation.

FIG. 7A is an explanatory diagram showing allowable tolerance of a shiftfrom the conjugate relation between the first diffractive element andthe second diffractive element.

FIG. 7B is an explanatory diagram of another aspect showing theallowable tolerance of a shift from the conjugate relation.

FIG. 8 is a ray diagram of the optical system.

FIG. 9 is a ray diagram of an optical system related to a first modifiedexample.

FIG. 10 is a ray diagram of an optical system related to a secondmodified example.

FIG. 11 is a ray diagram of an optical system related to a thirdmodified example.

FIG. 12 is a ray diagram of an optical system related to a fourthmodified example.

FIG. 13 is an explanatory diagram of a first optical section in theoptical system of the fourth modified example.

FIG. 14 is an explanatory diagram of an optical system related to asecond embodiment.

FIG. 15 is an explanatory diagram of an optical system related to athird embodiment.

FIG. 16 is an explanatory diagram of an optical system related to afourth embodiment.

FIG. 17 is a diagram in which an intermediate image is different inposition between a horizontal direction and a vertical direction.

FIG. 18 is an explanatory diagram of an optical system related to afifth embodiment.

FIG. 19 is an explanatory diagram of an optical system related to asixth embodiment.

FIG. 20 is an explanatory diagram of an optical system related to aseventh embodiment.

FIG. 21 is a diagram showing a roughly conjugate relation between afirst diffractive element and a second diffractive element in an opticalsystem related to an eighth embodiment.

FIG. 22 is an explanatory diagram of the light emitted from the seconddiffractive element in the roughly conjugate relation shown in FIG. 21 .

FIG. 23 is an explanatory diagram showing how the light shown in FIG. 22enters the eye.

DESCRIPTION OF EXEMPLARY EMBODIMENTS First Embodiment

An embodiment of the invention will hereinafter be described withreference to the accompanying drawings. It should be noted that in eachof the drawings described below, the scale sizes and angles of thelayers and the members are made different from the actual ones in orderto make the layers and the members have recognizable dimensions.

FIG. 1 is an appearance diagram showing an aspect of an appearance of adisplay device 100 according to the present embodiment. FIG. 2 is anappearance diagram showing an aspect of another appearance of thedisplay device 100. FIG. 3 is an explanatory diagram showing an aspectof an optical system 10 of the display device 100 shown in FIG. 1 . Itshould be noted that in FIG. 1 through FIG. 3 , the anteroposteriordirection with respect to an observer wearing the display device isdefined as a direction along a Z axis, the front of the observer wearingthe display device as one side in the anteroposterior direction isdefined as a front side Z1, and the rear of the observer wearing thedisplay device as the other side in the anteroposterior direction isdefined as a rear side Z2. Further, the horizontal direction withrespect to the observer wearing the display device is defined as adirection along an X axis, the right side of the observer wearing thedisplay device as one side in the horizontal direction is defined as aright side X1, and the left side of the observer wearing the displaydevice as the other side in the horizontal direction is defined as aleft side X2. Further, the vertical direction with respect to theobserver wearing the display device is defined as a direction along a Yaxis, the upper side of the observer wearing the display device as oneside in the vertical direction is defined as an upper side Y1, and thelower side of the observer wearing the display device as the other sidein the vertical direction is defined as a lower side Y2.

The device 100 shown in FIG. 1 is a head-mounted display device, and hasa right-eye optical system 10 a for making image light L0 a enter theright eye Ea, and a left-eye optical system 10 b for making image lightL0 b enter the left eye Eb. The display device 100 is formed to have ashape of, for example, a pair of eyeglasses. Specifically, the displaydevice 100 is further provided with a housing 90 for holding theright-eye optical system 10 a and the left-eye optical system 10 b. Thedisplay device 100 is mounted on the head of the observer with thehousing 90.

As the housing 90, the display device 100 is provided with a frame 91, atemple 92 a disposed on the right side of the frame 91 to be caught bythe right ear of the observer, and a temple 92 b disposed on the leftside of the frame 91 to be caught by the left ear of the observer. Theframe 91 has housing spaces 91 s in both side sections, and a variety ofparts such as an image light projection device constituting opticalsystems 10 described later are housed in the housing spaces 91 s. Thetemples 92 a, 92 b are foldably connected to the frame 91 with hinges95.

The right-eye optical system 10 a and the left-eye optical system 10 bare the same in basic configuration. Therefore, in the followingdescription, the right-eye optical system 10 a and the left-eye opticalsystem 10 b are each described as the optical system 10 without beingdiscriminated.

Further, although the image light L0 is made to proceed in thehorizontal direction along the X axis in the display device 100 shown inFIG. 1 , there is a case in which the image light L0 is made to proceedfrom the upper side Y1 toward the lower side Y2 to be emitted to theeyes E of the observer as shown in FIG. 2 , or the case in which thereis adopted a configuration of disposing the optical systems 10throughout the area from the top of the head to the front of the eyes E.

The basic configuration of the optical systems 10 of the display device100 will be described with reference to FIG. 3 . FIG. 3 is anexplanatory diagram showing an aspect of the optical system 10 of thedisplay device 100 shown in FIG. 1 . It should be noted that in FIG. 3 ,in addition to the light L1 (solid lines) of a specific wavelength ofthe image light L0, there are also illustrated the light L2(dashed-dotted lines) on the long-wavelength side and the light L3(dotted lines) on the short-wavelength side with respect to the specificwavelength.

As shown in FIG. 3 , in the optical system 10, a first optical sectionL10 having positive power, a second optical section L20 having positivepower, a third optical section L30 having positive power, and a fourthoptical section L40 having positive power are disposed along theproceeding direction of the image light L0 emitted from an image lightgeneration device 31.

In the present embodiment, the first optical section L10 having thepositive power is constituted by a projection optical system 32. Thesecond optical section L20 having the positive power is constituted by afirst diffractive element 50 of a reflective type. The third opticalsection L30 having the positive power is constituted by a light guidesystem 60. The fourth optical section L40 having the positive power isconstituted by a second diffractive element 70 of the reflective type.In the present embodiment, the first diffractive element 50 and thesecond diffractive element 70 are each the reflective type diffractiveelement.

In such an optical system 10, focusing attention to the proceedingdirection of the image light L0, the image light generation device 31emits the image light L0 toward the projection optical system 32, theprojection optical system 32 emits the image light L0 having entered theprojection optical system 32 toward the first diffractive element 50,and the first diffractive element 50 emits the image light L0 havingentered the first diffractive element 50 toward the light guide system60. The light guide system 60 emits the image light L0 having enteredthe light guide system 60 to the second diffractive element 70, and thenthe second diffractive element emits the image light L0 having enteredthe second diffractive element 70 toward the eye E of the observer.

In the present embodiment, the image light generation device 31generates the image light L0.

As the image light generation device 31, it is possible to adopt aconfiguration provided with a display panel 310 such as an organicelectroluminescence display element. According to such a configuration,it is possible to provide the display device 100 small in size andcapable of displaying an image high in image quality. Further, as theimage light generation device 31, it is possible to adopt aconfiguration provided with an illumination light source (not shown) andthe display panel 310 such as a liquid crystal display element formodulating illumination light emitted from the illumination lightsource. According to such a configuration, since it is possible toselect the illumination light source, there is an advantage that thedegree of freedom of the wavelength characteristics of the image lightL0 expands. Here, as the image light generation device 31, it ispossible to adopt a configuration having the single display panel 310capable of color display. Further, as the image light generation device31, it is also possible to adopt a configuration having the plurality ofdisplay panels 310 corresponding respectively to the colors, and acombining optical system for combining the image light of the respectivecolors emitted from the plurality of display panels 310 with each other.Further, as the image light generation device 31, it is also possible toadopt a configuration of modulating a laser beam with a micromirrordevice.

The projection optical system 32 is an optical system for projecting theimage light L0 generated by the image light generation device 31, and isconstituted by a plurality of lenses 321. In FIG. 3 , there is cited thecase of using the three lenses 321 in the projection optical system 32as an example, but the number of the lenses 321 is not limited to thisexample, and it is also possible for the projection optical system 32 tobe provided with four or more lenses 321. Further, it is also possiblefor the lenses 321 to be bonded to each other to constitute theprojection optical system 32. Further, it is also possible for the lens321 to be formed of a lens with a free-form surface.

The light guide system 60 has a lens system 61 which the image light L0having been emitted from the first diffractive element 50 enters, and amirror 62 for emitting the image light L0 having been emitted from thelens system 61 toward a direction tilted obliquely. The lens system 61is constituted by a plurality of lenses 611 disposed in theanteroposterior direction along the Z axis. The mirror 62 has areflecting surface 620 tilted obliquely toward the anteroposteriordirection. In the present embodiment, the mirror 62 is a totalreflection mirror. It should be noted that it is also possible to use ahalf mirror as the mirror 62, and in this case, it is possible to widenthe range in which the outside light can visually be recognized.

Then, a configuration of the first diffractive element 50 and the seconddiffractive element 70 will be described.

In the present embodiment, the first diffractive element 50 and thesecond diffractive element 70 are the same in basic configuration.Hereinafter, the description will be presented citing the configurationof the second diffractive element 70 as an example.

FIG. 4A is an explanatory diagram of interference stripes 751 of thesecond diffractive element 70 shown in FIG. 3 . As shown in FIG. 4A, thesecond diffractive element 70 is provided with a reflective volumeholographic element 75, and the reflective volume holographic element 75is a partial reflective diffractive optical element. Therefore, thesecond diffractive element 70 constitutes a combiner having a partialtransmissive reflective property. Therefore, since the outside lightalso enters the eye E via the second diffractive element 70, it ispossible for the observer to visually recognize the image in which theimage light L0 formed in the image light generation device 31 and theoutside light (the background) are superimposed on each other.

The second diffractive element 70 is opposed to the eye E of theobserver, and a plane of incidence 71 of the second diffractive element70 which the image light L0 enters has a concavely curved surfacerecessed toward a direction of getting away from the eye E. In otherwords, the plane of incidence 71 has a shape curved so that the centralpart is recessed with respect to the peripheral part in the incidentdirection of the image light L0. Therefore, it is possible toefficiently converge the image light L0 toward the eye E of theobserver.

The second diffractive element 70 has the interference stripes 751having a pitch corresponding to the specific wavelength. Theinterference stripes 751 are recorded on a holographic photosensitivelayer as a difference in refractive index, and the interference stripes751 are tilted toward one direction with respect to the plane ofincidence 71 of the second diffractive element 70 so as to correspond toa specific incident angle. Therefore, the second diffractive element 70diffracts to deflect the image light L0 toward a predetermineddirection. The specific wavelength and the specific incident anglecorrespond to the wavelength and the incident angle of the image lightL0. The interference stripes 751 having such a configuration can beformed by performing interference exposure on the holographicphotosensitive layer using reference light Lr and object light Ls.

In the present embodiment, the image light L0 is used for the colordisplay. Therefore, the second diffractive element 70 has theinterference stripes 751R, 751G and 751B each formed at the pitchcorresponding to the specific wavelength. For example, the interferencestripes 751R are formed at a pitch corresponding to red image light LRhaving a wavelength of, for example, 615 nm in a wavelength range of 580nm through 700 nm. The interference stripes 751G are formed at a pitchcorresponding to green image light LG having a wavelength of, forexample, 535 nm in a wavelength range of 500 nm through 580 nm. Theinterference stripes 751B are formed at a pitch corresponding to blueimage light LB having a wavelength of, for example, 460 nm in awavelength range of 400 nm through 500 nm. Such a configuration can beformed by performing the interference exposure on the holographicphotosensitive layer using the reference light LrR, LrG and LrB and theobject light LsR, LsG and LsB having respective wavelengths in the statein which the holographic photosensitive layers having sensitivitiescorresponding to the respective wavelengths are formed.

It should be noted that it is also possible to disperse thephotosensitive materials having sensitivities to the respectivewavelengths in the holographic photosensitive layer, and then form theinterference stripes 751 having the interference stripes 751R, 751G and751B superimposed in one layer as shown in FIG. 4B by performing theinterference exposure on the holographic photosensitive layer using thereference light LrR, LrG and LrB and the object light LsR, LsG and LsBhaving the respective wavelengths. Further, it is also possible to uselight of a spherical wave as the reference light LrR, LrG and LrB andthe object light LsR, LsG and LsB.

The first diffractive element 50 the same in basic configuration as thesecond diffractive element 70 is provided with a reflective volumeholographic element 55. The first diffractive element 50 has a concavelycurved surface which is a recessed surface as a plane of incidence 51which the image light L0 enters. In other words, the plane of incidence51 has a shape curved so that the central part is recessed with respectto the peripheral part in the incident direction of the image light L0.Therefore, it is possible to efficiently deflect the image light L0toward the light guide system 60.

FIG. 5 is an explanatory diagram showing the diffractive characteristicsof the first diffractive element 50 and the second diffractive element70 shown in FIG. 3 . FIG. 5 shows differences in diffraction anglebetween the specific wavelength and peripheral wavelengths in the casein which the light beam enters a point on the volume hologram. FIG. 5shows a shift in diffraction angle of the light with the peripheralwavelength having the wavelength of 526 nm with the solid line L526, andshows a shift in diffraction angle of the light with the peripheralwavelength having the wavelength of 536 nm with the dotted line L536assuming the specific wavelength as 531 nm. As shown in FIG. 5 , even inthe case in which the light beam enters the same interference stripesrecorded on the hologram, the longer the wavelength of the light beamis, the more largely the light beam is diffracted, and the shorter thewavelength of the light beam is, the more difficult for the light beamto be diffracted. Therefore, in the case of using the two diffractiveelements, namely the first diffractive element 50 and the seconddiffractive element 70, as in the present embodiment, the wavelengthcompensation cannot appropriately achieved unless the light beam is madeto enter the diffractive elements taking the light beam angles in thelong wavelength light and the short wavelength light into consideration.In other words, it becomes unachievable to cancel the color aberrationgenerated in the second diffractive element 70. Further, since thediffraction angle differs by the number of interference stripes, it isnecessary to take the interference stripes into consideration.

In the optical system 10 shown in FIG. 3 , as described in Document 1,since the incident direction to the second diffractive element 70 and soon have been optimized in accordance with whether the sum of the numberof times of the formation of the intermediate image between the firstdiffractive element 50 and the second diffractive element 70 and thenumber of times of the reflection by the mirror 62 is odd or even, it ispossible to achieve the wavelength compensation, namely cancel the coloraberration.

Specifically, as shown in FIG. 3 , the image light L0 having entered thefirst diffractive element 50 is diffracted by the first diffractiveelement 50 to thereby be deflected. On this occasion, the diffractionangle θ2 of the light L2 on the long wavelength side with respect to thespecific wavelength becomes larger than the diffraction angle θ1 of thelight L1 with the specific wavelength. Further, the diffraction angle θ3of the light L3 on the short wavelength side with respect to thespecific wavelength becomes smaller than the diffraction angle θ1 of thelight L1 with the specific wavelength. Therefore, it results in that theimage light L0 having been emitted from the first diffractive element 50is deflected for each wavelength to be dispersed.

The image light L0 having been emitted from the first diffractiveelement 50 enters the second diffractive element 70 via the light guidesystem 60, and is diffracted by the second diffractive element 70 tothereby be deflected. On this occasion, the formation of theintermediate image is performed once and the reflection by the mirror 62is performed once in the light path from the first diffractive element50 to the second diffractive element 70. Therefore, defining the anglebetween the image light L0 and the normal line of the plane of incidenceof the second diffractive element 70 as the incident angle, the light L2on the long wavelength side with respect to the specific wavelength hasthe incident angle θ12 larger than the incident angle θ11 in the lightL1 with the specific wavelength, and the light L3 on the shortwavelength side with respect to the specific wavelength has the incidentangle θ13 smaller than the incident angle θ11 in the light L1 with thespecific wavelength. Further, as described above, the diffraction angleθ2 of the light L2 on the long wavelength side with respect to thespecific wavelength becomes larger than the diffraction angle θ1 of thelight L1 with the specific wavelength, and the diffraction angle θ3 ofthe light L3 on the short wavelength side with respect to the specificwavelength becomes smaller than the diffraction angle θ1 of the light L1with the specific wavelength.

Therefore, although the light L2 on the long wavelength side withrespect to the specific wavelength enters the first diffractive element50 with a larger incident angle than that of the light L1 with thespecific wavelength, since the diffraction angle of the light L2 on thelong wavelength side with respect to the specific wavelength is largerthan the diffraction angle of the light L1 with the specific wavelength,as a result, the light L2 on the long wavelength side with respect tothe specific wavelength and the light L1 with the specific wavelengthbecome roughly parallel to each other when being emitted from the seconddiffractive element 70. In contrast, although the light L3 on the shortwavelength side with respect to the specific wavelength enters the firstdiffractive element 50 with a smaller incident angle than that of thelight L1 with the specific wavelength, since the diffraction angle ofthe light L3 on the short wavelength side with respect to the specificwavelength is smaller than the diffraction angle of the light L1 withthe specific wavelength, as a result, the light L3 on the shortwavelength side with respect to the specific wavelength and the light L1with the specific wavelength become roughly parallel to each other whenbeing emitted from the second diffractive element 70. In such a manneras described above, since the image light L0 having been emitted fromthe second diffractive element 70 enters the eye E of the observer asthe roughly parallel light as shown in FIG. 3 , the shift in imagelocation on a retina E0 between the wavelengths is suppressed.Therefore, it is possible to cancel the color aberration generated inthe second diffractive element 70.

Then, a conjugate relation between the first diffractive element 50 andthe second diffractive element 70 will be described.

FIG. 6A is an explanatory diagram of the case in which the firstdiffractive element 50 and the second diffractive element 70 are in theconjugate relation. FIG. 6B and FIG. 6C are each an explanatory diagramof the case in which the first diffractive element 50 and the seconddiffractive element 70 are not in the conjugate relation. FIG. 7A andFIG. 7B are explanatory diagrams showing an allowable tolerance of theshift from the conjugate relation between the first diffractive element50 and the second diffractive element 70 shown in FIG. 6B and FIG. 6C.In FIG. 7A and FIG. 7B, the light with the specific wavelength isrepresented by the solid lines Le, the light having the wavelength of(specific wavelength) −10 nm is represented by the dashed-dotted linesLf, and the light having the wavelength of (specific wavelength) +10 nmis represented by the dashed-two-dotted lines Lg. It should be notedthat in FIGS. 6A through 6C, FIG. 7A and FIG. 7B, the first diffractiveelement 50, the second diffractive element 70 and the light guide system60 are shown as ones of the transmissive type so that the procession ofthe light is easy to understand, and the first diffractive element 50,the second diffractive element 70 and the light guide system 60 arerepresented by the arrows.

As shown in FIG. 6A, in the case of making the first diffractive element50 and the second diffractive element 70 have the conjugate relation,the diverging light emitted from a point A (a first position) of thefirst diffractive element 50 is converged by the light guide system 60having the positive power, and then enters a point B (a second positioncorresponding to the first position) of the second diffractive element70. Therefore, the color aberration due to the diffraction generated atthe point B can be compensated at the point A.

In contrast, as shown in FIG. 6B and FIG. 6C, in the case in which thefirst diffractive element 50 and the second diffractive element 70 arenot in the conjugate relation, the diverging light emitted from thepoint A of the first diffractive element 50 is converged by the lightguide system 60 having the positive power, but enters the seconddiffractive element 70 so as to be focused at a position farther ornearer than the point B on the second diffractive element 70. Therefore,the point A and the point B are not in a one-to-one relation. Here,since the compensating effect increases in the case in which theinterference stripes in the area is uniform, in the case in which thefirst diffractive element 50 and the second diffractive element 70 arenot in the conjugate relation, the compensating effect weakens. Incontrast, it is difficult to compensate the entire projection area ofthe second diffractive element 70 with the first diffractive element 50.Therefore, in the case of the configuration shown in FIG. 6B and FIG.6C, the sufficient wavelength compensation cannot be performed, andtherefore, deterioration of the resolution occurs.

It should be noted that in the light having the wavelength in a range of±10 nm with respect to the specific wavelength, there exists an error ina range of about ±0.4 mm from the point B reached by the light with thespecific wavelength, but the deterioration of the resolution isinconspicuous. As a result of considering such an allowable range, inthe case in which the light is focused in front of the ideal point B onthe second diffractive element 70 reached by the light with the specificwavelength, and enters a range of ±0.8 mm from the point B as shown inFIG. 7A, the deterioration of the resolution is inconspicuous. Further,in the case in which the light is focused behind the ideal point B onthe second diffractive element 70 reached by the light with the specificwavelength, and enters the range of ±0.8 mm from the point B as shown inFIG. 7B, the deterioration of the resolution is inconspicuous.Therefore, in the first diffractive element 50 and the seconddiffractive element 70, even if the complete conjugate relation is notachieved, in the case in which the roughly conjugate relation isachieved, and the light reaches the range of ±0.8 mm from the idealpoint B, the deterioration of the resolution can be allowed. In otherwords, in the present embodiment, the expression that the firstdiffractive element 50 and the second diffractive element 70 have theconjugate relation means the fact that the incident position of thelight with the specific wavelength falls within the error range of ±0.8mm from the ideal incident point.

FIG. 8 is a ray diagram in the optical system 10 of the presentembodiment. In FIG. 8 and diagrams referred to later, the opticalsections arranged along the optical axis are represented by the thickarrows. Further, a light beam emitted from one pixel of the image lightgeneration device 31 is represented by the solid lines La, a principallight bean emitted from an end part of the image light generation device31 is represented by the dashed-dotted lines Lb, and a position havingthe conjugate relation with the first diffractive element 50 isrepresented by the long dotted lines Lc. Here, an “intermediate image”denotes a place where the light beam (the solid lines La) having beenemitted from the one pixel is focused, and a “pupil” denotes a placewhere the principal light beam (the dashed-dotted lines Lb) with eachfield angle is focused. Further, FIG. 8 shows the procession of thelight emitted from the image light generation device 31. It should benoted that in FIG. 8 , in order to simplify the drawings, all of theoptical sections are illustrated as ones of the transmissive type.

As shown in FIG. 8 , in the optical system 10 of the present embodiment,the first optical section L10 having the positive power, the secondoptical section L20 provided with the first diffractive element 50 andhaving the positive power, the third optical section L30 having thepositive power, and the fourth optical section L40 provided with thesecond diffractive element 70 and having the positive power are disposedalong the light path of the image light emitted from the image lightgeneration device 31.

The focal distance of the first optical section L10 is L/2, and thefocal distances of the second optical section L20, the third opticalsection L30, and the fourth optical section L40 are all L. Therefore,the optical distance from the second optical section L20 to the thirdoptical section L30 and the optical distance from the third opticalsection L30 to the fourth optical section L40 are equal to each other.

In such an optical system 10, a first intermediate image P1 of the imagelight is formed between the first optical section L10 and the thirdoptical section L30, a pupil R1 is formed between the second opticalsection L20 and the fourth optical section L40, a second intermediateimage P2 of the image light is formed between the third optical sectionL30 and the fourth optical section L40, and the fourth optical sectionL40 collimates the image light to form an exit pupil R2. On thisoccasion, the third optical section L30 arbitrarily controls the imagelight having been emitted from the second optical section L20 intodiverging light, converging light or parallel light, and then make theimage light enter the fourth optical section L40. The second opticalsection L20 makes the image light having been emitted from the firstoptical section L10 enter the third optical section L30 as converginglight. In the optical system 10 of the present embodiment, the pupil R1is formed in the vicinity of the third optical section L30 between thesecond optical section L2 and the fourth optical section L40. Thevicinity of the third optical section L30 means a position nearer to thethird optical section L30 than to the second optical section L20 betweenthe second optical section L20 and the third optical section L30, or aposition nearer to the third optical section L30 than to the fourthoptical section L40 between the third optical section L30 and the fourthoptical section L40.

Further, the third optical section L30 makes the light having theperipheral wavelength deflected by the first diffractive element 50 tobe shifted from the light having the specific wavelength enter apredetermined range of the second diffractive element 70 with respect tothe image light from the one point of the image light generation device31. In other words, the first diffractive element 50 and the seconddiffractive element 70 are in the conjugate relation or the roughlyconjugate relation. Here, an absolute value of the magnifying power ofthe projection on the second diffractive element 70 due to the thirdoptical section L30 of the first diffractive element 50 is in a rangefrom 0.5 times to 10 times, and is preferably in a range from the samesize to 5 times.

Therefore, according to the optical system 10 of the present embodiment,the first intermediate image P1 of the image light is formed between theprojection optical system 32 and the light guide system 60, the pupil R1is formed in the vicinity of the light guide system 60, the secondintermediate image P2 of the image light is formed between the lightguide system 60 and the second diffractive element 70, and the seconddiffractive element collimates the image light to form the exit pupilR2.

In the optical system 10 of the present embodiment, the firstintermediate image P1 is formed between the first optical section L10(the projection optical system 32) and the second optical section L20(the first diffractive element 50).

According to the optical system 10 of the present embodiment, the fourconditions (conditions 1, 2, 3 and 4) described below are fulfilled.

Condition 1: The light beam having been emitted from one point of theimage light generation device 31 is imaged on the retina E0 as onepoint.

Condition 2: The entrance pupil of the optical system and the pupil ofthe eyeball are conjugated.

Condition 3: The first diffractive element 50 and the second diffractiveelement 70 are appropriately arranged so as to compensate the peripheralwavelength.

Condition 4: The first diffractive element 50 and the second diffractiveelement 70 are in the conjugate relation or the roughly conjugaterelation.

More specifically, as is understood from the solid lines La shown inFIG. 8 , since the condition 1 that the light beam having been emittedfrom one point of the image light generation device 31 is imaged on theretina E0 as one point is fulfilled, it is possible for the observer tovisually recognize the one pixel. Further, as is understood from thesolid lines La shown in FIG. 8 , since the condition 2 that the entrancepupil of the optical system 10 and a pupil E1 of the eye E are in theconjugate relation (conjugate between pupils) is fulfilled, it ispossible to visually recognize the entire area of the image generated bythe image light generation device 31. Further, since the condition 3that the first diffractive element 50 and the second diffractive element70 are appropriately arranged so as to compensate the peripheralwavelength is fulfilled, the color aberration generated in the seconddiffractive element 70 can be canceled by performing the wavelengthcompensation. Further, as is understood from the long dotted lines Lcshown in FIG. 8 , since the condition that the first diffractive element50 and the second diffractive element 70 are in the conjugate relationor the roughly conjugate relation is fulfilled, it is possible to makethe light beam enter the place where the interference stripes are thesame between the first diffractive element 50 and the second diffractiveelement 70, and therefore, it is possible to appropriately perform thewavelength compensation. Therefore, it is possible to suppress thedeterioration of the resolution of the image light.

First Modified Example

FIG. 9 is a ray diagram of an optical system 10A related to a firstmodified example. As shown in FIG. 9 , in the optical system 10A of thepresent modified example, the first optical section L10 (the projectionoptical system 32) having the positive power, the second optical sectionL20 provided with the first diffractive element 50 and having thepositive power, the third optical section L30 (the light guide system60) having the positive power, and the fourth optical section L40provided with the second diffractive element 70 of a reflective type andhaving the positive power are disposed along the light path of the imagelight emitted from the image light generation device 31.

The focal distance of the first optical section L10 is 4L/11, the focaldistance of the second optical section L20 is 6L/11, the focal distanceof the third optical section L30 is 3L/4, and the focal distance of thefourth optical section L40 is L. Therefore, the ratio between theoptical distance from the second optical section L20 to the thirdoptical section L30 and the optical distance from the third opticalsection L30 to the fourth optical section L40 is 1:2, and the opticaldistance from the second optical section L20 to the third opticalsection L30 is shorter than the optical distance from the third opticalsection L30 to the fourth optical section L40. Therefore, even in thecase of reducing the size of the optical system 10, it is hard for thevision to be blocked by the third optical section L30.

Also in the present modified example, similarly to the configuration ofthe first embodiment described with reference to FIG. 8 , the firstintermediate image P1 of the image light is formed between the firstoptical section L10 and the third optical section L30, the pupil R1 isformed in the vicinity of the third optical section L30, the secondintermediate image P2 of the image light is formed between the thirdoptical section L30 and the fourth optical section L40, and the fourthoptical section L40 collimates the image light to form the exit pupilR2. In the present modified example, similarly to the configuration ofthe first embodiment, the first intermediate image P1 is formed betweenthe first optical section L10 (the projection optical system 32) and thesecond optical section L20 (the first diffractive element 50).

Also in the optical system 10A of the present modified example,similarly to the configuration of the first embodiment, the condition 1that the light beam having been emitted from one point of the imagelight generation device 31 is imaged on the retina E0 as one point isfulfilled. Further, the condition 2 that the entrance pupil of theoptical system 10A and the pupil E1 of the eye E are in the conjugaterelation (conjugate between the pupils) is fulfilled. Further, thecondition 3 that the first diffractive element 50 and the seconddiffractive element 70 are appropriately arranged is fulfilled. Further,since the condition 4 that the first diffractive element 50 and thesecond diffractive element 70 are in the conjugate relation or theroughly conjugate relation is fulfilled, it is possible to make thelight beam enter the place where the interference stripes are the samebetween the first diffractive element 50 and the second diffractiveelement 70, and therefore, it is possible to cancel the color aberrationby appropriately performing the wavelength compensation. Therefore, itis possible to suppress the deterioration of the resolution of the imagelight.

Second Modified Example

FIG. 10 is a ray diagram of an optical system 10B related to a secondmodified example. As shown in FIG. 10 , in the optical system 10B of thepresent modified example, the first optical section L10 (the projectionoptical system 32) having the positive power, the second optical sectionL20 provided with the first diffractive element 50 and having thepositive power, the third optical section L30 (the light guide system60) having the positive power, and the fourth optical section L40provided with the second diffractive element 70 of a reflective type andhaving the positive power are disposed along the light path of the imagelight emitted from the image light generation device 31. In the presentmodified example, a fifth optical section L50 is disposed between theimage light generation device 31 and the projection optical system 32.

Also in the present modified example, similarly to the configuration ofthe first embodiment described with reference to FIG. 8 , the firstintermediate image P1 of the image light is formed between the firstoptical section L10 and the third optical section L30, the pupil R1 isformed in the vicinity of the third optical section L30, the secondintermediate image P2 of the image light is formed between the thirdoptical section L30 and the fourth optical section L40, and the fourthoptical section L40 collimates the image light to form the exit pupilR2. Also in the present modified example, similarly to the configurationof the first embodiment, the first intermediate image P1 is formedbetween the first optical section L10 (the projection optical system 32)and the second optical section L20 (the first diffractive element 50).Specifically, in the case of defining the position where the image lightgeneration device 31 is disposed in the configuration of the firstembodiment described with reference to FIG. 8 as a virtual panelposition, in the configuration shown in FIG. 10 , the image lightgeneration device 31 is disposed on the opposite side to the firstoptical section L10 from the virtual panel position, and the distancebetween the image light generation device 31 and the first opticalsection L10 is longer than the distance between the image lightgeneration device 31 and the first optical section L10 in theconfiguration of the first embodiment described with reference to FIG. 8. Even in such a case, since the fifth optical section L50 is disposedbetween the image light generation device 31 and the projection opticalsystem 32, the light beam having been emitted from the image lightgeneration device 31 becomes substantially the same as in theconfiguration of the first embodiment described with reference to FIG. 8after reaching the first optical section L10.

Therefore, also in the optical system 10B of the present modifiedexample, similarly to the configuration of the first embodiment, thecondition 1 that the light beam having been emitted from one point ofthe image light generation device 31 is imaged on the retina E0 as onepoint is fulfilled. Further, the condition 2 that the entrance pupil ofthe optical system 10B and the pupil E1 of the eye E are in theconjugate relation (conjugate between the pupils) is fulfilled. Further,the condition 3 that the first diffractive element 50 and the seconddiffractive element 70 are appropriately arranged is fulfilled. Further,since the condition 4 that the first diffractive element 50 and thesecond diffractive element 70 are in the conjugate relation or theroughly conjugate relation is fulfilled, it is possible to make thelight beam enter the place where the interference stripes are the samebetween the first diffractive element 50 and the second diffractiveelement 70, and therefore, it is possible to cancel the color aberrationby appropriately performing the wavelength compensation. Therefore, itis possible to suppress the deterioration of the resolution of the imagelight.

Third Modified Example

FIG. 11 is a ray diagram of an optical system 100 related to a thirdmodified example. As shown in FIG. 11 , in the optical system 100 of thepresent modified example, the first optical section L10 (the projectionoptical system 32) having the positive power, the second optical sectionL20 provided with the first diffractive element 50 and having thepositive power, the third optical section L30 (the light guide system60) having the positive power, and the fourth optical section L40provided with the second diffractive element 70 of a reflective type andhaving the positive power are disposed along the light path of the imagelight emitted from the image light generation device 31.

Also in the present modified example, similarly to the configurations ofthe first embodiment, the first modified example and the second modifiedexample, the first intermediate image P1 of the image light is formedbetween the first optical section L10 and the third optical section L30,the pupil R1 is formed in the vicinity of the third optical section L30,the second intermediate image P2 of the image light is formed betweenthe third optical section L30 and the fourth optical section L40, andthe fourth optical section L40 collimates the image light to form theexit pupil R2.

In the present modified example, unlike the configurations of the firstembodiment, the first modified example and the second modified example,the first intermediate image P1 is formed between the second opticalsection L20 (the first diffractive element 50) and the third opticalsection L30 (the light guide system 60).

Also in such an optical system 100, similarly to the configuration ofthe first embodiment, the condition 1 that the light beam having beenemitted from one point of the image light generation device 31 is imagedon the retina E0 as one point is fulfilled. Further, the condition 2that the entrance pupil of the optical system 100 and the pupil E1 ofthe eye E are in the conjugate relation (conjugate between the pupils)is fulfilled. Further, the condition 3 that the first diffractiveelement 50 and the second diffractive element 70 are appropriatelyarranged is fulfilled. It should be noted that in the optical system 100of the present modified example, the condition 4 that the firstdiffractive element 50 and the second diffractive element 70 are in theconjugate relation or the roughly conjugate relation is not fulfilled.Even in this case, it is possible for the third optical section L30 tomake the light deflected by the first diffractive element 50 to beshifted from the light having the specific wavelength enter apredetermined range of the second diffractive element 70 with respect tothe image light from the one point of the image light generation device31. Therefore, the problem that the light enters the place different ininterference stripes is compensated by the third optical section L30.Therefore, it becomes possible for the light having the peripheralwavelength of the specific wavelength to enter the vicinity of the lightwith the specific wavelength, and it is possible to roughly cancel thecolor aberration by performing the wavelength compensation. Therefore,it is possible to suppress the deterioration of the resolution. In otherwords, according to the optical system 10C of the present modifiedexample, it is possible to obtain a certain wavelength compensationeffect in the case in which the aperture ratio is low although thewavelength compensation effect is low compared to the configuration ofthe first embodiment and so on.

Fourth Modified Example

FIG. 12 is a ray diagram of an optical system 10D related to a fourthmodified example. FIG. 13 is an explanatory diagram of the first opticalsection L10 related to the present modified example. As shown in FIG. 12, in the optical system 10D of the present modified example, similarlyto the configuration of the first embodiment described with reference toFIG. 8 , the first optical section L10 (the projection optical system32) having the positive power, the second optical section L20 providedwith the first diffractive element 50 and having the positive power, thethird optical section L30 (the light guide system 60) having thepositive power, and the fourth optical section L40 provided with thesecond diffractive element 70 of a reflective type and having thepositive power are disposed. Here, the image light generation device 31has a laser source 316, a collimating lens 317, and a micromirror device318, and the image is generated by driving the micromirror device 318 tothereby perform the scan with the laser source 316. Therefore, the imagelight generation device 31 itself forms the light of the field angle.

Therefore, as shown in FIG. 13 , compared to the case of forming thepupil between the lenses L11, L12 used in the first optical section L10in the configuration of the first embodiment described with reference toFIG. 8 , the image light generation device 31 and the lens L11 arereplaced with the laser source 316, the collimating lens 317 and themicromirror device 318 described above.

According to such an optical system 10D, in the case of wearing thedisplay device 100, even in the case in which a temperature changeoccurs due to the body heat and the heat of the display device 100itself to cause a variation in the spectrum width of the laser beam andso on, it is possible to display an image high in quality due to thewavelength compensation.

Second Embodiment

Then, a display device according to a second embodiment will bedescribed. The present embodiment relates to another configuration inthe optical system.

FIG. 14 is an explanatory diagram of the display device according to thesecond embodiment. An optical system 12 shown in FIG. 14 is disposedalong the vertical direction as shown in FIG. 2 , and the projectionoptical system 32, the first diffractive element 50 and the light guidesystem 60 are disposed in an area from the image light generation device31 disposed at the top of the head to the second diffractive element 70in front of the eye E. In the present embodiment, the light guide system60 is formed of a mirror 62 having a reflecting surface 620 recessed inthe central part from the peripheral part, and has positive power. Thereflecting surface 620 is formed of a spherical surface, asphericalsurface, or a free-form surface. In the present embodiment, thereflecting surface 620 is formed of the free-form surface. The firstdiffractive element 50 is formed of a transmissive volume holographicelement and a lens integrated with each other, and has positive power.It should be noted that the first diffractive element 50 itself isconfigured to have the positive power in some cases.

In the optical system 12 of the present embodiment, similarly to thefirst modified example described with reference to FIG. 9 , the firstoptical section L10 (the projection optical system 32) having thepositive power, the second optical section L20 provided with the firstdiffractive element 50 and having the positive power, the third opticalsection L30 (the mirror 62 of the light guide system 60) having thepositive power, and the fourth optical section L40 provided with thesecond diffractive element 70 of a reflective type and having thepositive power are disposed along the light path of the image lightemitted from the image light generation device 31. Therefore, the firstintermediate image P1 of the image light is formed between the firstoptical section L10 and the third optical section L30, the pupil R1 isformed in the vicinity of the third optical section L30, the secondintermediate image P2 of the image light is formed between the thirdoptical section L30 and the fourth optical section L40, and the fourthoptical section L40 collimates the image light to form the exit pupilR2.

Here, the third optical section L30 is constituted by the mirror 62having the positive power. Therefore, the diverging light having beendiffracted by the second optical section L20 is converged by the mirror62. Further, the light having been converged enters the point which thelight with the specific wavelength enters and the vicinity of the pointof the fourth optical section L40 (the second diffractive element 70).

Also in the optical system 12 of the present embodiment, similarly tothe first modified example described with reference to FIG. 9 , thecondition 1 that the light beam having been emitted from one point ofthe image light generation device 31 is imaged on the retina E0 as onepoint is fulfilled. Further, the condition 2 that the entrance pupil ofthe optical system 12 and the pupil E1 of the eye E are in the conjugaterelation (conjugate between the pupils) is fulfilled. Further, thecondition 3 that the first diffractive element 50 and the seconddiffractive element 70 are appropriately arranged is fulfilled. Further,since the condition 4 that the first diffractive element 50 and thesecond diffractive element 70 are in the conjugate relation or theroughly conjugate relation is fulfilled, it is possible to make thelight beam enter the place where the interference stripes are the samebetween the first diffractive element 50 and the second diffractiveelement 70, and therefore, it is possible to cancel the color aberrationby appropriately performing the wavelength compensation. Therefore, itis possible to suppress the deterioration of the resolution of the imagelight.

Third Embodiment

Then, a display device according to a third embodiment will bedescribed. The present embodiment relates to another configuration inthe optical system.

FIG. 15 is an explanatory diagram of the display device according to thethird embodiment. In the optical system 12 shown in FIG. 14 , the firstoptical section L10 (the projection optical system 32) and the secondoptical section L20 (the first diffractive element 50) are separatedfrom each other, but in an optical system 13 of the present embodiment,the first optical section L10 (the projection optical system) and thesecond optical section L20 (the first diffractive element 50) areintegrated with each other as shown in FIG. 15 . More specifically, thefirst optical section L10 (the projection optical system 32) is formedof a prism 85 provided with a plurality of reflecting surfaces 851, 852,and the second optical section L20 (the first diffractive element 50 ofa transmissive type) is provided to an exit surface 853 of the prism 85.

The rest of the configuration is common to the second embodimentdescribed with reference to FIG. 14 . Therefore, similarly to theconfiguration shown in FIG. 14 , the color aberration can be canceled byappropriately performing the wavelength compensation. Therefore, it ispossible to suppress the deterioration of the resolution of the imagelight. Further, since the first optical section L10 (the projectionoptical system 32) and the second optical section L20 (the firstdiffraction element 50) are integrated with each other using the prism85, it is possible to achieve reduction of assembling tolerance,reduction in size in the anteroposterior direction of the head, and soon.

Fourth Embodiment

Then, a display device according to a fourth embodiment will bedescribed. The present embodiment relates to another configuration inthe optical system.

FIG. 16 is an explanatory diagram of the display device according to thefourth embodiment. Similarly to the configuration described withreference to FIG. 1 and FIG. 3 , in an optical system 14 shown in FIG.16 , the projection optical system 32, the first diffractive element 50and the light guide system 60 are disposed in an area from the imagelight generation device 31 disposed at the side of the head to thesecond diffractive element 70 in front of the eye E. In the presentembodiment, the projection optical system 32 has a lens 326 having arotationally-symmetrical shape, and a lens 327 having a free-formsurface. The light guide system 60 is formed of the mirror 62 having thereflecting surface 620 recessed in the central part from the peripheralpart, and has positive power. The reflecting surface 620 is formed of aspherical surface, aspherical surface, or a free-form surface. In thepresent embodiment, the reflecting surface 620 is formed of thefree-form surface. The first diffractive element 50 is formed of areflective volume holographic element. A mirror 40 is disposed at anintermediate position in the light path starting from the projectionoptical system 32 and reaching the first diffractive element 50, and theprojection optical system 32 forms the intermediate image (the firstintermediate image P1) on the reflecting surface of the mirror 40 or inthe vicinity of the reflecting surface. The mirror 40 is provided with aconcavely curved surface as the reflecting surface 400, and has thepositive power. In the case in which the reflecting surface 400 of themirror 40 has the positive power, it is possible to arrange that themirror 40 is included in the constituents of the projection opticalsystem 32. In other words, in the case in which the mirror 40 has thepositive power, it is also possible to arrange that the first opticalsection L10 includes the mirror 40. It should be noted that it is alsopossible to adopt a configuration in which the reflecting surface 400 ofthe mirror 40 is formed as a flat surface and has no power.

In the optical system 14 configured in such a manner, similarly to thefirst modified example described with reference to FIG. 9 , the firstoptical section L10 (the projection optical system 32) having thepositive power, the second optical section L20 provided with the firstdiffractive element 50 and having the positive power, the third opticalsection L30 (the mirror 62 of the light guide system 60) having thepositive power, and the fourth optical section L40 provided with thesecond diffractive element 70 of a reflective type and having thepositive power are disposed along the light path of the image lightemitted from the image light generation device 31.

In the optical system 14 according to the present embodiment, the firstoptical section L10 includes the plurality of lenses 326, 327. The lens326 out of the plurality of lenses 326, 327 is a lens located thenearest to the image light generation device 31. Therefore, the lens 326corresponds to a “first lens.”

In the optical system 14 of the present embodiment, a pupil R0 is formedbetween the lens 326 and the lens 327 in the first optical section L10,the pupil R1 is formed in the vicinity of the third optical section L30,the second intermediate image P2 of the image light is formed betweenthe third optical section L30 and the fourth optical section L40, andthe fourth optical section L40 collimates the image light to form theexit pupil R2.

The first intermediate image P1 and the second intermediate image P2shown in FIG. 16 are each an intermediate image in the image lightspreading in the horizontal direction along the surface of the sheet.The image light having been emitted from the image light generationdevice 31 spreads not only in the horizontal direction but also in thevertical direction perpendicular to the surface of the sheet of FIG. 16, and therefore, there exists an intermediate image of the image lightspreading in the vertical direction. In the present embodiment, theintermediate image in the vertical direction exists in the vicinity ofthe intermediate image in the horizontal direction.

It should be noted that the first intermediate image P1 is formed in thevicinity of the mirror 40 in the optical system 14 of the presentembodiment, but can also be formed in the first optical section L10 (theprojection optical system 32).

Further, the intermediate image in the horizontal direction and theintermediate image in the vertical direction can also exist atrespective positions different from each other. FIG. 17 is a ray diagramin the case in which the position of the intermediate image in thehorizontal direction and the position of the intermediate image in thevertical direction are different from each other, and FIG. 17 is a raydiagram in the image light in the horizontal direction and the verticaldirection. In FIG. 17 , the reference symbol L_(H) denotes the imagelight in the horizontal direction, the reference symbol P1 _(H) denotesthe first intermediate image in the image light L_(H) in the horizontaldirection, the reference symbol L_(V) denotes the image light in thevertical direction, and the reference symbol P1 _(V) denotes the firstintermediate image in the image light L_(V) in the vertical direction.Further, in FIG. 17 , the image light generation device 31, the firstoptical section L10 (the projection optical system 32) and the mirror 40disposed along the optical axis are schematically shown. Further, inFIG. 17 , the shapes of the lenses 326, 327 constituting the projectionoptical system 32 are also simplified.

As shown in FIG. 17 , the first intermediate image P1 _(H) in thehorizontal direction is located in the vicinity of the mirror 40, andthe first intermediate image P1 _(V) in the vertical direction islocated closer to the first optical section L10 than the firstintermediate image P1 _(H) in the horizontal direction.

In FIG. 17 , there is shown the case in which the position of theintermediate image is different between the horizontal direction and thevertical direction in the first intermediate image P1, but it is alsopossible for the second intermediate image to be different in positionbetween the horizontal direction and the vertical direction. Further, inthe case in which the position of the intermediate image is differentbetween the horizontal direction and the vertical direction in the firstintermediate image P1, it is also possible that one of the firstintermediate image P1 _(H) and the first intermediate image P1 _(V) isformed in the first optical section L10 and the other of the firstintermediate image P1 _(H) and the first intermediate image P1 _(V) isformed outside the first optical section L10.

Also in the optical system 14 of the present embodiment, similarly tothe first modified example described with reference to FIG. 9 , thecondition 1 that the light beam having been emitted from one point ofthe image light generation device 31 is imaged on the retina E0 as onepoint is fulfilled. Further, the condition 2 that the entrance pupil ofthe optical system 10 and the pupil E1 of the eye E are in the conjugaterelation (conjugate between the pupils) is fulfilled. Further, thecondition 3 that the first diffractive element 50 and the seconddiffractive element 70 are appropriately arranged is fulfilled. Further,since the condition 4 that the first diffractive element 50 and thesecond diffractive element 70 are in the conjugate relation or theroughly conjugate relation is fulfilled, it is possible to make thelight beam enter the place where the interference stripes are the samebetween the first diffractive element 50 and the second diffractiveelement 70, and therefore, it is possible to cancel the color aberrationby appropriately performing the wavelength compensation. Therefore, itis possible to suppress the deterioration of the resolution of the imagelight.

Further, out of the members shown in FIG. 16 , as plastic, glass and soon constituting the light transmissive member, there is used an opticalmember having high dispersion and low dispersion combined with eachother. Further, since the mirror 62 is used as the third optical sectionL30, the achromatic state is provided in the first optical section L10.Therefore, since the centroid position of the optical system 14 isshifted to the rear side Z2, there is an advantage that the burden onthe nose of the user can be eased. Further, regarding the mirror 62, ifa semi-transmissive mirror layer or an angular selective mirror layer isformed on a transparent member such as transparent resin or glass usinga sputtering method or the like, it is possible to visually recognizethe outside view via the mirror 62.

Fifth Embodiment

Then, a display device according to a fifth embodiment will bedescribed. The present embodiment relates to another configuration inthe optical system.

FIG. 18 is an explanatory diagram of the display device according to thefifth embodiment. Similarly to the fourth embodiment described withreference to FIG. 16 , in an optical system 15 shown in FIG. 18 , theprojection optical system 32 (the first optical section L10), the mirror40, the first diffractive element 50 (the second optical section L20)and the mirror 62 (the third optical section L30) of the light guidesystem 60 are disposed in an area from the image light generation device31 disposed at the side of the head to the second diffractive element 70(the fourth optical section L40) in front of the eye E.

In the present embodiment, the mirror 40 and the mirror 62 are formed ondifferent surfaces of a common member 81. The rest of the configurationis common to the fourth embodiment shown in FIG. 16 . Therefore,similarly to the fourth embodiment shown in FIG. 16 , it is possible toappropriately perform the wavelength compensation. Further, since themirror 40 and the mirror 62 are provided to the common member 81, it ispossible to achieve the reduction of the assembling tolerance and so on.Further, since it is possible to decrease the number of the types of themetal molds for manufacturing the mirror, it is possible to achieve thereduction of the cost.

Sixth Embodiment

Then, a display device according to a sixth embodiment will bedescribed. The present embodiment relates to another configuration inthe optical system.

FIG. 19 is an explanatory diagram of the display device according to thesixth embodiment. Similarly to the fourth embodiment described withreference to FIG. 16 , in an optical system 16 shown in FIG. 19 , theprojection optical system 32 (the first optical section L10), the mirror40, the first diffractive element 50 (the second optical section L20)and the mirror 62 (the third optical section L30) of the light guidesystem 60 are disposed in an area from the image light generation device31 disposed at the side of the head to the second diffractive element 70(the fourth optical section L40) in front of the eye E.

In the present embodiment, the mirror 62 and the second diffractiveelement 70 are formed on different surfaces of a common member 82. Therest of the configuration is common to the fourth embodiment shown inFIG. 16 . Therefore, similarly to the fourth embodiment shown in FIG. 16, it is possible to appropriately perform the wavelength compensation.Further, since the mirror 62 and the second diffractive element 70 areprovided to the common member 82, it is possible to achieve thereduction of the assembling tolerance and so on. Further, since it ispossible to decrease the number of the types of the metal molds formanufacturing the mirror, it is possible to achieve the reduction of thecost.

Seventh Embodiment

Then, a display device according to a seventh embodiment will bedescribed. The present embodiment relates to another configuration inthe optical system.

FIG. 20 is an explanatory diagram of the display device according to theseventh embodiment. Similarly to the fourth embodiment described withreference to FIG. 16 , in an optical system 17 shown in FIG. 20 , theprojection optical system 32 (the first optical section L10), the mirror40, the first diffractive element 50 (the second optical section L20)and the mirror 62 (the third optical section L30) of the light guidesystem 60 are disposed in an area from the image light generation device31 disposed at the side of the head to the second diffractive element 70(the fourth optical section L40) in front of the eye E.

In the present embodiment, the mirror 40, the mirror 62 and the seconddiffractive element 70 are formed on different surfaces of a commonmember 83. The rest of the configuration is common to the fourthembodiment shown in FIG. 16 . Therefore, similarly to the fourthembodiment shown in FIG. 16 , it is possible to appropriately performthe wavelength compensation. Further, since the mirror 40, the mirror 62and the second diffractive element 70 are provided to the common member83, it is possible to achieve the reduction of the assembling toleranceand so on. Further, since it is possible to decrease the number of thetypes of the metal molds for manufacturing the mirror, it is possible toachieve the reduction of the cost.

Eighth Embodiment

Then, a display device according to an eighth embodiment will bedescribed. The present embodiment relates to another configuration inthe optical system. In an optical system of the present embodiment, thefirst diffractive element 50 and the second diffractive element 70 arein the roughly conjugate relation. The roughly conjugate relationbetween the first diffractive element 50 and the second diffractiveelement 70 will hereinafter be described.

FIG. 21 is an explanatory diagram showing the roughly conjugate relationbetween the first diffractive element 50 and the second diffractiveelement 70 in an optical system 18 of the present embodiment. FIG. 22 isan explanatory diagram of the light emitted from the second diffractiveelement 70 in the roughly conjugate relation shown in FIG. 21 . FIG. 23is an explanatory diagram showing how the light shown in FIG. 22 entersthe eye E. It should be noted that in FIG. 21 , the light with thespecific wavelength is represented by the solid lines Le, the lighthaving the wavelength of (specific wavelength) −10 nm is represented bythe dashed-dotted lines Lf, and the light having the wavelength of(specific wavelength) +10 nm is represented by the dashed-two-dottedlines Lg. In FIG. 23 , how the light (the light represented by thedashed-dotted lines Lf in FIG. 22 ) having the wavelength of (specificwavelength) −10 nm enters the eye E is shown on the leftmost side of theobserver of the drawing, how the light (the light represented by thedashed-two-dotted lines Lg in FIG. 22 ) having the wavelength of(specific wavelength) +10 nm enters the eye E is shown on the rightmostside of the observer of the drawing, and how the light having thewavelength varied from (specific wavelength) −10 nm to (specificwavelength) +10 nm enters the eye E is shown therebetween. It should benoted that how the light with the specific wavelength enters the eye Eis not shown in FIG. 23 , but how the light with the specific wavelengthenters the eye E corresponds to an intermediate condition between thethird condition from the left and the fourth condition from the left.

Although in the embodiment and so on described above, it is preferableto make the first diffractive element 50 and the second diffractiveelement 70 have the conjugate relation, the first diffractive element 50and the second diffractive element 70 are made to have the roughlyconjugate relation as described above in the present embodiment. In thiscase, as shown in FIG. 21 , in the light having the peripheralwavelength shifted from the specific wavelength, the state when enteringthe second diffractive element 70 is different. Here, in the seconddiffractive element 70, the closer to the optical axis it becomes, thesmaller the number of the interference stripes becomes, and the weakerthe power for deflecting the light becomes. Therefore, by making thelight on the long wavelength side enter the optical axis side, andmaking the light on the short wavelength side enter the end side, thelight with the specific wavelength and the light with the peripheralwavelength are collimated, and therefore, it is possible to obtainsubstantially the same advantage as that of the wavelength compensation.

In this case, since the light beam position is shifted in accordancewith the wavelength, the diameter of the light beam entering the pupilincreases from the diameter ϕa to the diameter ϕb as shown in FIG. 22 .FIG. 23 shows the condition of the intensity of the light beam enteringthe pupil on this occasion. As is understood from FIG. 23 , although itis unachievable to fill the pupil in the vicinity of the specificwavelength, the light with the peripheral wavelength enters the positionshifted from the position of the light with the specific wavelength, andcan therefore fill the pupil diameter. As a result, it is possible toobtain the advantage that it becomes easy for the observer to observethe image.

Application to Other Display Devices

Although in the embodiment described above, there is illustrated thehead-mounted display device 100, it is also possible to apply theinvention to a head-up display, a hand-held display, an optical systemfor a projector, and so on.

The entire disclosure of Japanese Patent Application No.: 2018-011313,filed Jan. 26, 2018 and 2018-203691, filed Oct. 30, 2018 are expresslyincorporated by reference herein.

What is claimed is:
 1. A display device comprising: an image lightgeneration device; a projection optical system; a first diffractiveelement; a first mirror; and a second diffractive element, wherein theprojection optical system, the first diffractive element, the firstmirror and the second diffractive element are disposed along a lightpath of image light emitted from the image light generation device, afirst intermediate image of the image light is formed in the light pathbetween the projection optical system and the first mirror, a pupil isformed between the first diffractive element and the second diffractiveelement, a second intermediate image of the image light is formedbetween the first mirror and the second diffractive element, an exitpupil is formed by the second diffractive element, the first diffractiveelement and the second diffractive element are in a conjugate relation,and light emitted from a first position in the first diffractive elemententers a range of ±0.8 mm with respect to a second positioncorresponding to the first position in the second diffractive element.2. The display device according to claim 1, wherein the firstintermediate image is formed between the projection optical system andthe first diffractive element.
 3. The display device according to claim1, wherein the first mirror makes light of a field angle in the imagelight emitted from the first diffractive element enter the seconddiffractive element as diverging light.
 4. The display device accordingto claim 3, wherein the first mirror makes light diffracted by the firstdiffractive element to be shifted from light with a specific wavelengthenter a predetermined range of the second diffractive element withrespect to light corresponding to one point of an image generated by theimage light generation device.
 5. The display device according to claim3, wherein the first diffractive element makes the image light emittedfrom the projection optical system enter the first mirror as converginglight.
 6. The display device according to claim 3, wherein a plane ofincidence of the second diffractive element is a concavely curvedsurface recessed in a central part from a peripheral part, and thesecond diffractive element collimates the image light emitted from thefirst mirror.
 7. The display device according to claim 1, wherein anabsolute value of magnifying power of projection on the seconddiffractive element due to the first diffractive element is in a rangefrom 0.5 times to 10 times.
 8. The display device according to claim 7,wherein the absolute value of the magnifying power is in a range from asame size to 5 times.
 9. The display device according to claim 1,wherein an optical distance between the first diffractive element andthe first mirror is shorter than an optical distance between the firstmirror and the second diffractive element.
 10. The display deviceaccording to claim 1, wherein when the pupil is between the firstdiffractive element and the mirror, the pupil is nearer to the mirrorthan to the first diffractive element, and when the pupil is between themirror and the second diffractive element, the pupil is nearer to themirror than to the second diffractive element.
 11. The display deviceaccording to claim 1, further comprising a second mirror reflects theimage light from the projection optical system toward the firstdiffractive element.
 12. A display device comprising: an image lightgeneration device; a projection optical system including a first lensand a second lens; a first diffractive element; a first mirror; and asecond diffractive element, wherein the projection optical system, thefirst diffractive element, the first mirror and the second diffractiveelement are disposed along a light path of image light emitted from theimage light generation device, a first intermediate image of the imagelight is formed in the light path between the first lens located closestto the image light generation device and the first mirror, a pupil isformed between the first diffractive element and the second diffractiveelement, a second intermediate image of the image light is formedbetween the first mirror and the second diffractive element, an exitpupil is formed by the second diffractive element, and an opticaldistance between the first diffractive element and the first mirror isshorter than an optical distance between the first mirror and the seconddiffractive element.
 13. The display device according to claim 12,wherein the first intermediate image is formed in the projection opticalsystem.
 14. The display device according to claim 12, wherein when thepupil is between the first diffractive element and the mirror, the pupilis nearer to the mirror than to the first diffractive element, and whenthe pupil is between the mirror and the second diffractive element, thepupil is nearer to the mirror than to the second diffractive element.15. The display device according to claim 12, further comprising asecond mirror reflects the image light from the projection opticalsystem toward the first diffractive element.
 16. A display devicecomprising: an image light generation device; a projection opticalsystem including a first lens and a second lens; a first diffractiveelement; a first mirror; and a second diffractive element, wherein theprojection optical system, the first diffractive element, the firstmirror and the second diffractive element are disposed along a lightpath of image light emitted from the image light generation device, afirst intermediate image of the image light is formed in the light pathbetween the first lens located closest to the image light generationdevice and the first mirror, a pupil is formed between the firstdiffractive element and the second diffractive element, a secondintermediate image of the image light is formed between the first mirrorand the second diffractive element, an exit pupil is formed by thesecond diffractive element, the first diffractive element and the seconddiffractive element are in a conjugate relation, and light emitted froma first position in the first diffractive element enters a range of ±0.8mm with respect to a second position corresponding to the first positionin the second diffractive element.